Catheter deliverable foot implant and method of delivering the same

ABSTRACT

Methods and devices are disclosed for manipulating alignment of the foot to treat patients with flat feet, posterior tibial tendon dysfunction and metatarsophalangeal joint dysfunction. An inflatable implant is positioned in or about the sinus tarsi and/or first metatarsal-phalangeal joint of the foot. The implant is insertable by minimally invasive means and inflatable through a catheter or needle. Inflation of the implant alters the range of motion in the subtalar or first metatarsal-phalangeal joint and changes the alignment of the foot.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/068,675 filed on Mar. 1, 2005, which claims priority under35 U.S.C. §119(e) to U.S. Provisional Application No. 60/549,767 filedon Mar. 3, 2004, the disclosure of which are incorporated by referenceherein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of subtalar joint andfirst metatarsal-phalangeal implants for treating foot conditionsincluding flat feet, adult posterior tibial tendon dysfunction andmetatarsophalangeal joint dysfunction.

2. Description of the Related Art

Pes valgo planus, or flat foot, is a common condition where the arch ofa foot is weakened and is unable to properly support the weight of thebody. With a flat foot, shock absorption is reduced and misalignment ofthe foot occurs. These changes may eventually result in foot and anklepain, tendonitis, plantar fasciitis and hallux valgus, hallux limitusand functional disorders of the knees, hips and back. Although there areseveral causes of flat feet, one frequent cause is excessive motion inthe subtalar joint of the foot.

As early as 1946, surgeons have been attempting to apply thearthroereisis concept to the subtalar joint. Arthroereisis is a surgicalprocedure for limiting motion in a joint in cases of excessive mobility.One early method was to remedy abnormal excursion of the talus on thecalcaneus with the talus contacting the floor of the sinus tarsi byusing an “abduction block” procedure. During the abduction blockprocedure, a wedge-shaped bone graft was impacted into the anteriorleading edge of the posterior facet of the calcaneus. Impacting such abone graft prevented excessive inferior displacement of the talus uponthe calcaneus, thus limiting the amount of excess pronation of thesubtalar joint.

A pronation limiting osteotomy in the form of a lateral opening wedge ofthe posterior facet was developed for treatment of “flatfoot” incerebral palsy patients in 1964. In order to prevent interfering withsubtalar joint motion, a wedge-like bone graft was used to improve theweight-bearing alignment of the calcaneus. In 1970, an accessory bonegraft placed in the sinus tarsi was developed as a corrective procedure.Later, the bone graft was replaced with a silastic plug. As early as1976, a high molecular weight polyethylene plug was developed. The plugis cemented into the calcaneal sulcus against a resected portion of theposterior calcaneal facet. This procedure, known as “STA-peg” (subtalararthroereisis-peg), is a commonly used subtalar joint arthroereisisprocedure. STA-peg does not block excessive pronation, but rather altersthe axis of motion of the subtalar joint.

In addition, in 1976, a high molecular weight, polyethylene, threadeddevice known as a “Valenti Sinus Tarsi Arthroereises Device” wasinvented. The procedure used to implant the Valenti device is commonlyreferred to as the “Valenti” procedure. Unlike the STA-peg procedure,the Valenti procedure is an extra-articular procedure that involvesplacing the Valenti device into the sinus tarsi to block the anteriorand inferior displacement of the talus. Such placement of the Valentidevice does not restrict normal subtalar joint motion, but does blockexcessive pronation and resulting sequelae. The Valenti device has afrusto-conical shape and threads on the outer surface of the device,which allow it to be screwed into the sinus tarsi. Because of the shapeof the Valenti device, the greater the penetration of the device intothe sinus tarsi, the more the sinus is dilated and the more calcanealeversion is eliminated.

However, several problems reduce the desirability of the Valentiprocedure and device. Because of its frusto-conical shape and the mannerin which it is inserted, the Valenti device is difficult to preciselyposition in the subtalar joint and difficult to ensure that the properamount of calcaneal eversion has been eliminated. Furthermore, it isgenerally difficult to locate the device properly within the tarsalcanal because the implant must be threaded at least 3 to 5 millimetersmedial to the most lateral aspect of the posterior facet for correctplacement. Because of its polyethylene construction, the device cannotbe imaged using radiography (X-ray) to determine whether the properposition has been achieved.

More recent attempts to control subtalar motion in the hyperpronatedfoot include the Maxwell-Brancheau arthroereisis (MBA), the Kalixsubtalar prosthesis and the Futura arthroereisis. The MBA is a titaniumalloy implant where the implantation procedure involves insertion“trial” implants to determine the proper size of the actual implantused. The MBA implant procedure requires either general anesthesia orlocal anesthesia with sedation. It also requires up to a ¾ inch incisionon the lateral portion of the foot. The MBA implant uses a metal guidepin for positioning the implant. The guide pin must be positioned withextreme care to prevent damage to the calcaneus. A two-week period ofcrutch use and foot immobilization typically follows the procedure. TheKalix implant is a cone-shaped implant with limited expansion ability.The operator can use a double screwdriver to increase the diameter ofthe implant. The Kalix implant requires two weeks of non-weight bearingand three to four weeks of immobilization following implantation of thedevice.

Another site of frequent foot problems is the firstmetatarsal-phalangeal joint. The first metatarsal-phalangeal joint (MTP)is a complex joint of the foot where bones, tendons and ligaments worktogether to transmit and distribute the body's weight, especially duringmovement. Bunions are the first MTP joint disorder most frequentlytreated by podiatric surgeons. First-line treatment involves educatingpatients about the condition and evaluating their footwear. Providerscan direct their patients to wear wider, low-heeled shoes, use bunionpads, apply ice and take over-the-counter analgesic medications. Theseoptions are designed to relieve pain and make it easier to walk andengage in physical activities, but they do not address the underlyingcause of bunions.

Bunions usually occur from inherited faulty biomechanics that putabnormal stress on the first MTP joint. Contrary to popular belief,bunions are aggravated, not caused, by shoes. Various non-surgicalapproaches can help prevent aggravation of bunions and other MTP-relatedproblems. For some patients, non-surgical treatment is sufficient, butsurgical intervention is considered if the bunions are progressive or ifnon-operative treatments provide inadequate improvement.

Bunion surgery is performed to repair tendons and other soft tissue andremove a small amount of bone. Procedures to correct more severe bunionsmay involve removal of the bump or minor realignment of the big toejoint. The most severe and disabling bunions often require extensivejoint realignment, reconstruction, implants or joint replacement.Significant morbidity and recuperation time is required for suchprocedures.

First MTP-related problems also occur from repetitive trauma to the areaand from arthritis. Over time, active persons can put continuous stresson the first MTP joint that eventually wears out the cartilage and leadto the onset of arthritis. This condition, known as hallux rigidus,causes loss of movement and pain in the joint. In most situations,non-operative treatments can be prescribed to provide relief, but thosewith advanced disease might need surgery, especially when the protectivecovering of cartilage deteriorates, leaving the joint damaged and withdecreased range of motion. Again, significant morbidity results fromthese procedures and an extended recovery time is required.

SUMMARY OF THE INVENTION

In one embodiment, the invention is a subtalar joint implant, comprisingan inflatable balloon adapted for positioning in the sinus tarsi of afoot. In another embodiment, the invention is a foot implant comprisingan inflatable balloon, wherein the inflatable balloon is adapted forextra-articular positioning in the sinus tarsi of the foot.

In one embodiment of the invention, a method for treating a patient isprovided. The method comprises providing an inflatable subtalar implantfor the procedure, inserting the implant into the sinus tarsi of a food,inflating the implant with an inflation material and changing thealignment of the hindfoot. Furthermore, the insertion of the implantinto the sinus tarsi may be performed through a cannula inserted intothe sinus tarsi. The inflation material may be a fluid or a solid. Oneexample of a solid inflation material are microspheres. In otherembodiments of the invention, multiple agents may be used to inflate theimplant, such as a substrate and catalyst capable of solidifying. Insome embodiments, the multiple agents are combined before inflation ofthe implant. In other embodiments, the multiple agents are combinedduring inflation of the implant.

In another embodiment of the invention, another method for treating apatient is provided. This method comprises providing an inflatablesubtalar implant for the procedure, identifying a foot having a firstrange of motion, inserting the implant into the sinus tarsi of the footand adapting the foot to a second range of motion by inflating theimplant.

In still another embodiment of the invention, another method fortreating a patient is provided. This method comprises providing aninflatable subtalar implant, identifying a foot having a firstweight-bearing alignment, changing the foot to a second weight-bearingalignment, inserting the implant into the sinus tarsi of the foot andsecuring the foot in the second weight-bearing alignment by inflatingthe implant. The first and second weight-bearing alignments may bedefined by the angle formed between a first line connecting the edges ofan articular surface of the talus and a second line connecting the edgesof an articular surface of a navicular bone. Alternatively, the firstand second weight-bearing alignments may be defined by the angle betweenthe long axis of the talus and a second line along the long axis of thefirst metatarsal bone. Still another alternative is to define the firstand second weight-bearing alignments by the angle between the first linebetween most plantar point of a calcaneus and the most inferior point ofthe distal articular surface of the calcaneus, and a second line withina horizontal plane of the patient. Still another alternative is todefine the first and second weight-bearing alignments by the anglebetween a first line along the plantar border of the calcaneus and asecond line along a first midpoint in the body of a talus and a secondmidpoint in the neck of the talus.

Several embodiments of the invention provide a minimally invasive methodfor treating a patient. This method comprises providing an inflatablesubtalar implant, inserting the implant into the sinus tarsi of a foot,inflating the implant, changing the range of motion of the subtalarjoint of the foot and conforming the implant to the shape of the sinustarsi thereby.

Some embodiments of the invention provide a method for treating apatient, comprising identifying a cyma line in a foot of a patient,smoothing the cyma line and securing the smoothing by inflating animplant in the sinus tarsi of the foot.

In another embodiment of the invention, a method for treating a patientis provided, comprising accessing the sinus tarsi of a foot through anaccess path having a cross sectional diameter of no more than about 0.5inches, where the sinus tarsi have a talus and calcaneus spaced apart bya first minimum distance. The space between the talus and calcaneus isincreased to a second minimum distance and the talus and calcaneus isthen restrained at the second minimum distance.

In another embodiment, another method for treating a patient isprovided, comprising providing an inflatable first metatarsal-phalangealjoint implant, inserting the implant into a first metatarsal-phalangealjoint of a foot and inflating the implant with a fluid.

Several embodiments of the invention provide these advantages, alongwith others that will be further understood and appreciated by referenceto the written disclosure, figures, and claims included herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure and method of making the invention will be betterunderstood with the following detailed description of embodiments of theinvention, along with the accompanying illustrations, in which:

FIG. 1 is a superior elevation view of the calcaneus;

FIG. 2 is a lateral elevation view of the talo-calcaneus relationship;

FIG. 3 is a lateral elevation view of the foot bones showing the sinustarsi;

FIG. 4 is dorso-plantar elevation view of the foot showing the outlineof the sinus tarsi;

FIG. 5A is a superior elevation view of the ligament attachment sites tothe calcaneus; FIG. 5B is a coronal cross-section view showing theligaments of the sinus tarsi;

FIGS. 6A and 6B depict the axis of rotation for the subtalar joint;

FIGS. 7A and 7B are schematic views of the motion of the subtalar jointas a mitered hinge joint;

FIGS. 8A and 8B are schematic views of subtalar joint motion as athreaded screw joint;

FIGS. 9A and 9B are posterior cross-sectional views of a neutrallyaligned and a hyperpronated foot;

FIGS. 10A and 10B are lateral radiographs of the foot illustrating thecyma lines in a neutrally aligned and misaligned foot, respectively;

FIGS. 11A and 11B are AP radiographs of the foot illustrating the cymalines in a neutrally aligned and misaligned foot, respectively;

FIGS. 12A and 12B are AP radiographs of the foot depicting thetalonavicular coverage angles in a neutrally aligned and misalignedfoot, respectively;

FIGS. 13A and 13B are lateral radiographs of the foot depicting lateraltalocalcaneal angles in a neutrally aligned and misaligned foot,respectively;

FIGS. 14A and 14B are lateral radiographs of the foot depicting thecalcaneal pitch angles in a neutrally aligned and misaligned foot,respectively;

FIGS. 15A and 15B are AP radiographs of the foot depictingAP-talar-first metatarsal angles in a neutrally aligned and misalignedfoot, respectively;

FIGS. 16A and 16B are lateral radiographs of the foot depicting thelateral talocalcaneal angles in a neutrally aligned and misaligned foot,respectively;

FIGS. 17A and 17B are AP radiographs of the foot depicting APtalocalcaneal angles in a neutrally aligned and misaligned foot,respectively;

FIGS. 18A and 18B are schematic coronal cross-sectional views of aneutrally aligned and hyperpronated foot, respectively. FIG. 18C is aschematic view depicting the effect of material placed within the sinustarsi. FIG. 18D is a schematic view depicting the tendency of the talusand calcaneus to cause displacement of material in the sinus tarsi;

FIGS. 19A and 19B are schematic longitudinal cross-sectional views ofthe talus and calcaneus in a hyperpronated foot before and afterinsertion of material into the sinus tarsi;

FIGS. 20A and 20B are side elevation and cross-sectional views of oneembodiment of the implant;

FIGS. 21A through 21H depict side elevation views of various embodimentsof non-conforming implants;

FIGS. 22A and 22B are elevation and cross sectional views of oneembodiment of the invention having a ridged outer surface;

FIGS. 23A and 23B are cross-sectional views of the foot with variousembodiments of barbs for anchoring the implant;

FIGS. 24A and 24B represent various embodiments of the inventioncomprising multiple inflatable compartments;

FIGS. 25A and 25B are elevation views of one embodiment of the couplinginterface and the distal end of a complementary delivery catheter. FIG.25C is a cross-sectional view of the implant in FIGS. 25A and 25Battached to a delivery catheter;

FIGS. 26A and 26B are elevation views of another embodiment of thecoupling interface and the distal end of a complementary deliverycatheter. FIG. 26C is a cross-sectional view of the implant in FIGS. 26Aand 26B attached to a delivery catheter;

FIGS. 27A through 27C depict one embodiment of the delivery system;

FIGS. 28A and 28B are schematic cross-sectional views of the foot beforeand after inflation of the sizing catheter;

FIG. 29 is a side elevation view of a foot following insertion of thedelivery catheter;

FIGS. 30A and 30B are schematic cross-sectional views of the foot withthe implant inserted; FIG. 30A shows an uninflated implant attached tothe delivery catheter and FIG. 30B depicts an inflated implant with thedelivery catheter removed;

FIG. 31A is a front elevation view of one embodiment of a first MTPjoint inflatable implant and FIG. 31B is a side cross-sectional view ofthe implant in FIG. 31A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The talus and calcaneus form the bones of the hindfoot. The talus is abone with no muscular attachments, but is stabilized by ligaments andcradled by the tendons passing from the leg to the foot. As shown inFIG. 1, the calcaneus 2 articulates with the talus at the calcanealanterior 4, middle 6 and posterior facets 8. FIG. 2 depicts therelationship between the talus 10 and calcaneus 2 and the talo-calcanealsurfaces 12, 14 that articulate with the midfoot bones. FIGS. 3 and 4depict the midfoot bones, including the navicular 16, cuboid 18 andcuneiform bones 20, 22, 24. The sinus tarsi 26, also known as thetalocalcaneal sulcus, is an extra-articular anatomic space between theinferior neck 28 of the talus 10 and the superior aspect of the distalcalcaneus 2. The space continues with the tarsal canal, a funnel ortrumpet-shaped space that extends medially to a small opening posteriorto the sustentaculum tali. Sinus tarsi 26 is oriented obliquely from alateral distal opening to proximal medial end. The canal is widerlaterally and narrower medially, but the lateral opening of the canal iscapable of widening with foot supination and narrowing with pronation.Fat and ligaments occupy the space and are perfused by the tarsal canalartery, a branch of the posterior tibial artery.

FIG. 5A is a superior view of the calcaneus 2 showing the ligamentattachments within the tarsal canal, including the inferior attachments30, 32, 34 of the extensor retinaculum 36 of the foot, the interosseoustalocalcaneal ligament 38 and the cervical ligament 40. The primaryligament is interosseous talocalcaneal ligament 38, shown in a coronalcross section of the foot in FIG. 5B. Its primary function is tomaintain apposition of the talus 10 to the calcaneus 2. The interosseoustalocalcaneal ligament 38 is anterior to the posterior subtalar jointand extends from calcaneus 2 to talus 10. It forms a transversepartition between the sulcus tali and the sulcus calcaneus, the twogrooves forming the sinus tarsi. Interosseus ligament 38 separatesanterior 4 and middle facets 6 of the calcaneal portion of the anteriorsubtalar joint from the posterior facet 8 of the posterior subtalarjoint and provides stability to the hindfoot. The cervical ligament 40,like the other ligaments of the tarsal sinus 26, is extra-capsular.Cervical ligament 40 is larger than interosseous talocalcaneal ligament38. It attaches to the cervical tubercle of the inferior and lateralaspects of neck 28 of talus 10 and the dorsal aspect of calcaneus 2medial to the origin of the extensor digitorum brevis muscle. Cervicalligament 40 is flattened, its width being four times greater than itsthickness. The primary function of cervical ligament 40, along withinterosseous talocalcaneal ligament 38, is to limit inversion of thehindfoot. The inferior extensor retinaculum 36 is a Y shaped strap offlat thick connective tissue that crosses the proximal portion of thefoot. The stem of the “Y” is composed of superficial and deep laminaethat enclose the long extensor tendons and prevent bow stringing of thelong extensor tendons. Laterally, inferior extensor retinaculum 36 isanchored to talus 10 and calcaneus 2 by ligament-like roots that arelocated in the tarsal sinus and canal. The medial 30, intermediate 32and lateral roots 34 together constitute the majority of the ligamentousmaterial in the tarsal sinus 26. Inferior extensor retinaculum 36assists cervical ligament 40 in limiting inversion of the subtalarjoint. Medial root 30 attaches to calcaneus 2 just anterior to theattachment site of interosseous talocalcaneal ligament 38. Medial root30 has a secondary attachment site to talus 10 in common withinterosseous talocalcaneal ligament 38. Intermediate root 32 attaches tocalcaneus 2 posterior to the attachment site of cervical ligament 40.Lateral root 34 attaches to calcaneus 2 at the external aspect of thetarsal sinus 26.

Subtalar motion is generally described as a rotational motion of thetalus around the calcaneus. FIGS. 6A and 6B depict the subtalar axis ofrotation 42, which typically extends upward and forward at an angle ofabout forty-two degrees from the floor at the heel. The axis deviatessixteen degrees medially from the midline of the foot. Generally, thesubtalar joint can be inverted about twenty degrees and everted aboutfive degrees. The average range of motion throughout the stance phase ofgait, however, is only about six degrees. Longitudinal translation inboth the proximal and distal directions is also associated with therotation movement, but the direction and magnitude of this movement ishighly variable in each person. Some researchers have characterized themotion of the subtalar joint as a mitered hinge joint 44, as shown inFIGS. 7A and 7B. The vertical member 46 is analogous to the leg and thehorizontal member 48 is analogous to the foot. Other researchers,however, have characterized the motion of the subtalar joint as a screwjoint, as shown in FIGS. 8A and 8B. The differences between thecharacterizations of the subtalar joint underscore the high degree ofvariation in the configuration of the joint within the population.

When an excessive range of motion exists in the subtalar joint,misalignment of the foot can occur. Compared to a person with aneutrally aligned foot, shown in FIG. 9A, a person with flat feet, shownin FIG. 9B, has a subtalar joint that is capable of eversion up to aboutsix degrees from a neutral talo-calcaneal alignment. Excessive eversionplaces increased stress upon the foot arch. Over time, foot or ankledisorders can develop from the misalignment. Misalignment of thesubtalar joint also affects the alignment of the bones in the midfootdue to the dependence of midfoot stability on hindfoot stability.

Alignment of the foot can be assessed on plain film x-ray imaging byexamining the cyma lines of the foot. The term “cyma line” refers to thejoining of two curved lines. A neutrally aligned foot forms a smoothcyma line (shown with dots) between the talonavicular joint and thecalcaneocuboid joint on radiographs in both the lateral and AP views, asshown in FIGS. 10A and 11A, respectively. If the cyma line is broken, asshown in FIGS. 10B and 11B, this finding suggests misalignment of thetalus 10 on the calcaneus 2 as seen in patients with flat feet.

Other radiographic methods of assessing foot alignment are alsoavailable. FIGS. 12A and 12B depict the evaluation of talonavicularuncoverage. Talonavicular uncoverage is an indication of forefootabduction, a component of flatfoot. This measurement is taken from aweight-bearing AP view. This angle represents the degree of shift ofnavicular 16 on talus 10. Two lines are drawn, one connecting the edgesof the articular surface 52 of the talus 10, and one connecting theedges of the articular surface 54 of the navicular 16. The angle formedby these two lines is the talonavicular coverage angle, as seen in FIG.12A. An angle of greater than 7 degrees indicates lateral talarsubluxation, shown in FIG. 12B. A more direct measurement of pes planus,or collapse of the longitudinal arch, is the talar-first metatarsalangle (Meary's angle), shown in FIGS. 13A and 13B. This is an angleformed between the long axis of the talus 2 and first metatarsal 56 on aweight-bearing lateral view. This line is used as a measurement ofcollapse of the longitudinal arch 50. Collapse may occur at thetalonavicular joint, naviculo-cuneiform, or cuneiform-metatarsal joints.In the normal weight-bearing foot, shown in FIG. 13A, the midline axisof the talus 2 is in line with the midline axis of the first metatarsal56. An angle that is greater than 4° convex downward is considered pesplanus. An angle of fifteen to thirty degrees, as in FIG. 13B, isconsidered moderate flat foot, and an angle greater than 30° isconsidered severe flat foot. FIGS. 14A and 14B depict radiographsevaluating the calcaneal inclination angle, or calcaneal pitch. A lineis drawn from the plantar-most surface of the calcaneus 2 to theinferior border of the distal articular surface. The angle createdbetween this line and the transverse plane, or the line from the plantarsurface of the calcaneus 2 to the inferior surface of the fifthmetatarsal head, is the calcaneal pitch, shown in FIG. 14A. A decreasedcalcaneal pitch is consistent with pes planus, as represented in FIG.14B. There have been differing opinions between researchers concerningthe normal range of calcaneal pitch. Eighteen to twenty degrees isgenerally considered normal, although measurements ranging fromseventeen to thirty-two degrees have also been reported to be normal.FIGS. 15A and 15B depict radiographs evaluating the AP-talar-firstmetatarsal angle. A line drawn through the mid-axis of the talus 10should be in line with the first metatarsal shaft 56, as in FIG. 15A. Ifthe line is angled medial to the first metatarsal 56 it indicates pesplanus, as illustrated in FIG. 15B. FIGS. 16A and 16B depict radiographsevaluating the lateral talocalcaneal angle. The lateral talocalcanealangle is the angle formed by the intersection of a first line bisectingthe talus 10 with a second line along the plantar border or through thelong axis of the calcaneus 2. The first line is drawn through twomidpoints in talus 10, one at the body and one at the neck. The angle isformed by the intersection of these axes. As shown in FIG. 16A, thenormal range is 25-45 degrees. An angle over 45 degrees indicateshindfoot valgus, another component of pes planus, as depicted in FIG.16B. FIGS. 17A and 17B depict radiographs evaluating the APtalocalcaneal angle, also known as Kite's angle. This is the angleformed by the intersection of a line bisecting the head and neck oftalus 10 and a line running parallel with the lateral surface ofcalcaneus 2. FIG. 17A depicts a foot within the range of normal foradults between 15-30°. Referring to FIG. 17B, an angle greater than 30°indicates hindfoot valgus, another component of pes planus.

FIGS. 18A and 18B are schematic cross-sectional representations throughthe sinus tarsi of a neutrally aligned foot compared to a hyperpronatedfoot, respectively. Due to ligament laxity, the hyperpronated foot has agreater range of motion at talus 10 and calcaneus 2, which causes ashift in load bearing along the medial portion of the foot and tends toflatten the arch. Insertion of material 58 into sinus tarsi 26, altersthe range of subtalar motion and limits the range of pronation. FIG. 18Cshows that material 58 positioned in sinus tarsi 26 can have awedge-type effect to position calcaneus 2 to a neutral alignment. FIG.18D illustrates, however, that over time, the configuration of talus 10and calcaneus 2 also has a tendency to cause lateral displacement ofmaterial 58 through forces exerted onto material inserted into sinustarsi 26. FIGS. 19A and 19B are schematic longitudinal cross-sectionalrepresentations of a hyperpronated foot before and after insertion ofmaterial 58 into sinus tarsi 26.

Accordingly, one embodiment of the present invention provides an implant60 which can be easily located within the tarsal canal, which may or maynot deform under post-operative compressive forces, which would ensurethat the desired amount of calcaneal eversion has been provided afterinsertion of the implant 60 and which can be imaged using radiography todetermine whether the implant has been properly positioned during theprocedure. By placing a device into the tarsal space between talus 10and calcaneus 2, hindfoot motion and stability may be favorablymodified. Such a device may further provide midfoot stability becausemidfoot-stability is co-dependent on hindfoot stability. Dysfunction ofthe posterior tibial tendon that supports the foot arch may also betreated by restoring the arch of the foot and relieving the excessivetension on the tendon.

By developing a minimally invasive, catheter-deliverable subtalarimplant, disruption of the joint capsule and the ligamentous structuresin and around the lateral portion of the foot can be reduced. Currentsubtalar implants require either transection of the ligaments overlyingthe sinus tarsi or the dilation of an opening up to about ¾ inchdiameter through the ligaments. Dilation of this magnitude will stretchand disrupt the ligaments. In general, the implant in accordance withthe present invention may be advanced through a tissue opening of nogreater than about 7 mm, and preferably no greater than about 2 mm toabout 3 mm.

The development of an inflatable, non-metallic implant will allow thecreation of an in-situ customized prosthesis that will also minimizetrauma to the surrounding tissue during the implantation procedure andwith long-term use. This will considerably shorten the postoperativerecuperation period compared to existing devices and reducepostoperative pain and swelling. Moreover, because the integrity of thetissue overlying the sinus tarsi is preserved through minimally invasiveimplantation, the intact tissue is able to assist in anchoring theimplant in the sinus tarsi. By customized, the inventor contemplates animplant that is at least partially conformable to the anatomical cavityin which it resides, at least prior to any polymerization or othercuring step.

In one embodiment of the invention, illustrated in FIGS. 20A and 20B,the implant 60 comprises an inflatable compartment 64 and an inflationport 66. Inflation port 66 provides access to compartment 64 withoutcompromising the integrity of compartment 64 and causing leakage. In oneembodiment of the invention, implant 60 will form a custom shape thatapproximates the shape of sinus tarsi 26. The custom shape is defined onits superior-medial surface 61 by the inferior surface of talus 10, onits inferior-medial surface 63 by the superior surface of calcaneus 2,and on its lateral surface 65 by soft tissue structures including thefascia. It is preferred, but not required, that the shape have a largelateral surface area 68. A large lateral surface takes advantage of theintact ligaments and soft tissue along the lateral border of sinus tarsi26 to hold implant 60 in place. The implant has a lateral surface area68 of between about 2 square centimeters to about 5 square centimeters,preferably between about 3 square centimeters to about 4 squarecentimeters, and more preferably about 3.8 square centimeters. Acustom-shaped implant 60 is also better adapted to affect the highlyvariable anatomy of the subtalar joint and to alter the highly variablegeometry and motion of the joint. A custom-shaped implant can beconfigured to have a greater contact surface area with sinus tarsi 26and can disperse the loading of the subtalar joint across a greatersurface area compared to non-customized implants. The size and shape ofsinus tarsi 26 is also varies with foot position. Therefore, the surgeonwill position the foot during the procedure based upon the anatomy of aparticular patient and the characteristics of the selected implant. Oneembodiment of the implantation procedure is described in detail below.

Generally, the area of the lateral-proximal surface 68 of the implantwill be at least about twice the cross-sectional area of the dilatedtissue access tract. Often, the lateral surface area will be at least5×, 8×, 10× or 20× or more than the access tract to resist migration ofthe implant.

In another embodiment, the implant is semi-customizable. The surgeon isable to limit certain dimensions or features of the semi-customizableimplant by selecting a balloon having a shorter length, diameter and/orvolume. The implant shape is further adjusted by allowing a variabledegree of inflation. Variable inflation may allow deeper positioning ofthe implant within the sinus tarsi by providing implant 60 with asmaller diameter for deeper insertion into the narrow tarsal canal.

In still another embodiment, the implant shape is preselected by thesurgeon. The implant is compressible onto a catheter for minimallyinvasive delivery, but assumes a preconfigured shape with inflation. Apreconfigured shape may be advantageously used to force a particularfoot alignment or to facilitate anchoring of the implant. One indicationfor this implant and procedure is the hyperpronated, flexible andreducible flatfoot. The most common patient with this indication ispediatric, but adults with posterior tibial tendon dysfunction orhyper-pronation in the absence of subtalar joint and mid tarsal jointarthritis are also eligible. FIGS. 21A through 21H represent implants ofvarious possible shapes for nonconforming implants. The implant can bespherical 70, cylindrical 72, conical 74, frusta-conical 76,wedge-shaped 78, helical 80, polyhedral 82 or any three-dimensionalshape 84 capable of positioning in the sinus tarsi. FIG. 21H is oneembodiment of implant 60 advantageously fitted to the sinus tarsi 26 ofa left foot. The implant, when inflated, may include a groove 86 orcavity dimensioned for fitting around the cervical ligament 40 and adistal tip 88 for anchoring implant 60 in a narrowing of the sinus tarsi26 along the interosseous ligament 38. A large lateral surface area 68uses the soft tissue at the lateral opening of the sinus tarsi 26 tomaintain the desired position of the implant. This implant has a lengthof about fifteen millimeters to about twenty millimeters, a lateraldiameter of about ten to about fifteen millimeters and a medial diameterof about six to about eight millimeters.

The outer surface 90 of implant 60 may be smooth, textured or compriseany of a variety of protrusions or indentations to reduce the risk ofimplant migration. FIGS. 22A and 22B show one embodiment of theinvention with a plurality of ridges 92 on the outer surface. Texturingon the outer surface 90 of implant 60 may provide an interference fit orincreased friction between implant 60 and sinus tarsi 26 to resistdisplacement of implant 60 from its desired position. In a furtherembodiment, the outer surface 90 may further comprise cellular ingrowthregions that allow ingrowth of the surrounding tissue and further resistdisplacement of the implant. The pore size of the cellular ingrowthregions may range from about 20 μm to about 100 μm or greater.Desirably, the porosity of the cellular ingrowth regions ranges from 20μm to 50 μm and, in many embodiments, the porosity of the cellularingrowth regions ranges from 20 μm to 30 μm.

If more aggressive anchoring of the implant is desired, the inflatablemember may be further configured to facilitate attachment of implant 60to soft tissue or bone. In one embodiment, sutures, clips, staples,tacks, pins, hooks, barbs, or other securing structures that can atleast partially penetrate the surrounding tissue or bone are used. Thesesecuring structures may be made from a variety of materials, includingmetals, polymers, ceramics or absorbable materials. Absorbable materialsinclude but are not limited to polylactic acid (PLA) or copolymers ofPLA and glycolic acid, or polymers of p-dioxanone and1,4-dioxepan-2-one. A variety of absorbable polyesters ofhydroxycarboxylic acids may be used, such as polylactide, polyglycolideand copolymers of lactide and glycolide, as described in U.S. Pat. Nos.3,636,956 and 3,297,033, which are hereby incorporated in their entiretyherein by reference. The use of absorbable materials allows the securingstructure to dissolve or resorb into human tissue after a known orestablishable time range, from a week to over a year.

In one non-limiting example, shown in FIG. 23A, a distal anchor 94 withat least two or three or four or more barbs 96 is attached to the medialsurface 98 of implant 60 for anchoring at the medial portion of thesinus tarsi 26. In another non-limiting example in FIG. 23B, one or moreshort pointed barbs 96 are integrally formed with implant 60 or securedthereto using any of a variety of attachment techniques which aresuitable depending upon the composition of implant 60. As the implant isinserted into sinus tarsi 26, barbs 96 penetrate the surrounding softtissue, bone or ligaments. Hooks may also be attached to or integrallyformed with implant, so that the implant can be hooked into thesurrounding tissue, possibly in combination with the use of abioadhesive. Such hooks and barbs may be formed from a bioabsorbable ordissolvable material as has discussed above.

In one embodiment of the invention, implant 60 comprises any of avariety of flexible materials that resist stretching. These materialsinclude but are not limited to polyethylene, polyolefins, polyvinylchloride, polyester, polyimide, polyethylene terephthalate (PET),polyamides, nylon, polyurethane and other polymeric materials. Oneskilled in the art can select the material based upon the desiredcompliance, biocompatability, rated burst pressure and other desiredcharacteristics. In one embodiment, the inflatable member has a wallthickness of about 0.001 cm to about 0.05 cm. In another embodiment, theinflatable member has a thickness of about 0.02 cm to about 0.03 cm.Generally, the inflatable member has a rated burst pressure of greaterthan 60 atmospheres (ATM) for resisting bursting and extrusion ofinflation material under physiologic loading. In another embodiment, theinflatable member has a rated burst pressure of at least about eight ATMor more. A lower burst pressure can be used where a curable material isused to inflate the inflatable member and will bear the loading of thesubtalar joint. In a further embodiment of the invention, implant 60 isintegrally formed with deformable wire supports within the material usedto form the inflatable member. One possible function of the wire supportto provide some stiffness to the implant during the insertion process toallow the operator to insert the implant into distal sulci or crevicesof the sinus tarsi. A wire support can also comprise a shape memorymetal, such as nitinol. Upon insertion of the implant into the sinustarsi, the body heat of the patient will cause the wire support tochange shape and expand to the borders of the sinus tarsi. Those skilledin the art understand that any of a variety of biocompatible, deformablemetals may be used to form the skeleton.

In addition to providing access to inflate the inflatable compartment,the inflation port may comprise other features to facilitate use of theimplant. The inflation port may be self-sealing or have a one-way valveto obviate the need for a separate sealing of the implant afterinflation. Valve configurations include but not limited tohemostatic-type valves, flap valves or duckbill valves. In someembodiments, a pierceable septum may be used. A flap valve 100 is shownin FIG. 20B. The flapper portion of the valve can be formed fromsilicone, rubber, neoprene or any other flexible material known to thosewith skill in the art. Less flexible materials may be used for the valvewhere the inflation fluid is highly viscous or curable. One skilled inthe art can select the type of seal based upon the inflation pressuresof the implant, the viscosity of the inflation fluid, curability andother characteristics. Inflation port 66 may be further configured tominimize any leakage of material from either implant 60 or the deliverysystem during the detachment process. Inflation port 66 may includeradio-opaque markers to allow a clinician to later deflate or adjustimplant 60 transcutaneously with a hypodermic needle.

The material used to inflate inflatable compartment 62 includes any of avariety of biocompatible materials, including but not limited to saline,silicone polymers, polyurethane polymers, linear or branched polyols,PMMA or others known in the art. Solid materials, such as smallpolymeric metallic microspheres, microtubules or microdiscs can also beused as a filling agent. The material can also be a combination ofmaterials, such a curable liquid substrate and a catalyst, that cansolidify within implant 60. Several U.S. patents disclose various typesof polymers or proteins that, assertedly, can be injected into a jointas a liquid or semi-liquid composition that subsequently harden into asolidified material. For example, U.S. Pat. No. 5,556,429 (Felt 1996),herein incorporated by reference, discloses injection of a fluidizedmixture of a biocompatible polymer (such as a silicone or polyurethanepolymer) and a biocompatible “hydrogel” (a hydrophilic polymer, formedby steps such as using an agent such as ethylene dimethacrylate tocross-link a monomer containing a hydroxyalkyl acrylate ormethacrylate), into a space. After injection, the polymer and hydrogelmixture can be set into solidified form by means such as ultravioletradiation, which can be introduced into the space by a fiber opticdevice. Other articles on surgically implantable polymers is containedin numerous published items; recent review articles include Peppas et al1994, Hubbell 1995, Stokes 1995, Burg et al 1997, Lewis 1997, Kim andMooney 1998, and Ambrosio et al 1998, herein incorporated by reference.Other discussions of biocompatible implantable materials are alsoavailable in various textbooks, such as Silver 1994, herein incorporatedby reference. Other combinations of inflation materials may include theaddition of iodine, barium or other radio-opaque component. One skilledin the art can select the desired material based upon the viscosity,density, cure time, degree of exothermic cure reaction, radio-opacityand other characteristics. For curable materials, one skilled in the artmay consider the load-bearing strength, tensile strength, shearstrength, fatigue, impact absorption, wear characteristics and otherfactors of the cured material.

In another embodiment, implant 60 has multiple inflation ports andmultiple compartments such that different portions of implant 60 can beindependently inflated. FIGS. 24A and 24B are non-limiting examples oftwo-compartment inflatable members. The delivery catheter for an implantcomprising multiple compartments may have multiple fluid ports to allowindependent inflation of the compartments. Different compartments may beinflated with different materials having different characteristics. Inone embodiment of the invention, implant 60 has an inner compartment 104and an outer compartment 106. Outer compartment 106 may be inflated witha curable material to provide a solid material at the surface of implant60. Inner compartment 104 may be inflated with a liquid material toprovide limited deformability to implant 60. Alternatively, outercompartment 106 may be inflated with a liquid material and innercompartment 104 is inflated with a curable material. This particularembodiment may provide cushioning to the joint surfaces by providing acompressible implant surface, yet the curable core provides someresilience to complete compression.

Implant 60 further comprises a coupling interface 108 that releasablyattaches implant 60 to the delivery system. Coupling interface 108 isgenerally located on or about inflation port 66 and allows for inflationof implant 60 through the delivery system without leakage of materialinto the surrounding tissue. Coupling interface 108 also allowstransmission of force, including torque, from the delivery system to theimplant to facilitate positioning of implant 60. Coupling interface 108is configured to allow detachment of implant 60 from the delivery systemand, optionally reattachment of the delivery system FIGS. 25A through25C illustrate one embodiment of the invention, where coupling interface108 comprises a flange 110 surrounding inflation port 66. Flange 110 iscapable of being grasped by prongs 112 extending from the deliverycatheter 114. Coupling interface 108 further comprises a base 116 havinga polygonal or otherwise rotationally keyed cross-section. Base 116 maybe positioned between coupling interface 108 and inflatable compartment64 and is capable of forming another mechanical interfit with an outersheath 146 over catheter 114. This additional mechanical interfitprovides further resistance to dislodging or separation of implant 60from delivery catheter 114 during implantation, especially fromrotational forces. FIGS. 26A through 26C depict another embodiment ofcoupling interface 108, comprising base 116 and an internal threadedlumen 118 for accepting a threaded core 120 extending from the deliverycatheter 114. The attachment of coupling interface 108 to deliverycatheter 114 is described in further detail below.

One embodiment of the delivery system is illustrated in FIGS. 27Athrough 27C, comprising a cannula or sheath 122, a sizing catheter 124with an inflatable balloon tip 126 and delivery catheter 114 attachableto implant 60. Cannula 122 is made from plastic with radio-opaquemarkers to allow imaging of the cannula. Cannula 122 can be introducedinto the sinus tarsi over a needle 130. Cannula 122 has a length ofabout two inches to about six inches and a diameter of about 12 gauge toabout 18 gauge. A lumen 128 is provided in cannula 122 to allow passageof sizing catheter 124 and delivery catheter 114 with attached implant60. Alternatively, the cannula can be made of metal and has a distal tipsufficiently sharp to pierce the skin, connective tissue and ligamentsoverlying the sinus tarsi. A metal cannula with a sharp tip would notrequire insertion of the cannula over a needle or guidewire.

Sizing catheter 124, shown in FIG. 27B, has a length of about two inchesto about eight inches and a diameter capable of passing through cannula122. Sizing catheter 124 has radiographic markers for determining itsposition in the foot during radiographic imaging. The proximal end 132of sizing catheter 124 comprises a Luer fitting 134 or other similartype of mechanical lock for attaching a syringe 136. A lumen 138 withinthe sizing catheter 124 provides a conduit from syringe 136 to sizingballoon tip 126 at the distal end of sizing catheter 124. Sizing balloontip 126 has a length of about fifteen millimeters and a diameter ofabout six to about twelve millimeters. Sizing balloon tip 126 can haveany of a variety of shapes similar to those described for implant 60.Syringe 136 has markings so that the volume of fluid inflated intosizing balloon tip 126 can be measured quantitatively. Sizing catheter124 is capable of performing a number of functions. Insertion of sizingcatheter 124 through cannula 122 initiates the dilatation of sinus tarsi26 and helps to prepare the path for introduction of permanent implant60. By filling sizing catheter balloon 126, the surgeon is able todetermine the volume of non-compressible fluid required to fill sinustarsi 26 to the proper degree necessary for selection of theconfiguration of permanent implant 60 capable of controlling pronationwithin the proper range.

Alternatively, sizing balloon 126 may comprise a high-compliancematerial that is capable of conforming to the surrounding anatomicalstructures. By filling sizing balloon 126 with a radio-opaque fluidunder fluoroscopy or with radiography, the surgeon can determine theproper three-dimensional shape and of the cavity 26. An implant 60 canbe selected to correspond with the predetermined shape and/or size. FIG.28A is a cross-sectional schematic of high-compliance sizing balloon 126inflated in sinus tarsi 26. As the balloon 126 is inflated in FIG. 28B,loose ligaments and connective tissue will be displaced while balloon126 conforms around taut structures. This shape information permitsselection or construction of an implant having a predetermined shape ordetermination of the need for a semi-customizable or fully customizableimplant.

In an alternative embodiment of the delivery system, sizing catheter 124is omitted because the inflation characteristics of the implant allowimplant 60 to be adapted to structural variations of the anatomy.Selection of a particular size or shape of implant is not required inthis alternative embodiment. In this embodiment, the surgeon canpartially inflate the implant, evaluate the effect on the foot alignmentand flexibility, and continue to inflate, deflate and/or position theimplant until a desired result is achieved. The delivery catheter 114may then be detached and withdrawn, leaving the implant 60 in place.

FIG. 27C shows one embodiment of delivery catheter 114, comprising aproximal end 140, a body 142, a distal end 144 and an outer sheath 146.The delivery catheter has a length of about two inches to about teninches and has a diameter capable of passing through cannula 122.Catheter 114 may contain radiographic markers for determining itsposition in the foot with imaging. Proximal end 140 of delivery catheter114 comprises at least one Luer fitting 134 or other similar type ofmechanical lock for attaching a syringe to inflate the implant withmaterial. Body 142 of delivery catheter 114 comprises at least one lumen148 to provide a conduit from the syringe or other source to implant 60fastened to distal end 144 of delivery catheter 114. A multi-lumencatheter may be used where the implant has multiple compartments, orwhere multiple reactive materials are used to inflate the implant. Theuse of multiple lumens may prevent reactive components of the implantmaterial from reacting within the catheter and prevent clogging of thecatheter. For inflation materials that use ultra-violet light forcuring, a fiber-optic line can be inserted through the lumen 148 toprovide the ultra-violet light. Outer sheath 146 comprises an innersurface 150, an outer surface 152, a proximal portion 154 and a distalportion 156. Outer sheath 146 also has a retracted position that exposesthe distal end 144 of delivery catheter 114 and an extended positionthat covers distal end 144 of delivery catheter 114.

Distal end 144 of delivery catheter 114 comprises an inflation lumen 158and a coupler for attaching to coupling interface 108 of implant 60. Inthe embodiment of the invention seen in FIG. 25A, where couplinginterface 108 comprises flange 110, the coupler 160 of delivery catheter114 comprises a plurality of radially outward-biased graspers or prongs112 extending distally. Graspers 112 may comprise bent wires, thinarcuate sheets, or any other configuration known to those with skill inthe art that is capable of engaging flange 110 and applying a proximallydirected force to flange 110. Referring back to FIG. 27C, when outersheath 146 of delivery catheter 114 is in the extended position, innersurface 150 of outer sheath 146 will contact prongs 112 and applyradially inward forces against prongs 112. These forces move the prongs112 closer together and allow the prongs 112 to engage the edge offlange 110 on implant 60.

If outer sheath 146 is further extended, inner surface 150 of sheath 146will contact base 116 of coupling interface 108. Base 116 of implant 60has a polygonal cross-section capable of forming a mechanical interfitwith a polygonal cross-section of inner surface 150 of outer sheath 146.Distal portion 156 of sheath 146 will also exert a distally directedcounterforce on implant 60 in opposition to the proximally directedforce on the implant from the prongs 112 to firmly attach implant 60 tothe delivery catheter 114. If sheath 146 is retracted, the mechanicalinterfit with base 116 is relieved and radially inward forces on prongs112 are removed. Prongs 112 will resume their outward bias and distractfrom flange 110 of implant 60, causing release of implant 60. Aspreviously mentioned, delivery catheter 114 shown in FIG. 26C, mayalternatively comprise a slideable inner core 161 within the inflationlumen 158 of delivery catheter 114 that is capable of extending throughcoupling interface 108 to engage inflation port 66 of implant 60. Alumen 162 in inner core 161 provides a conduit to inflate attachedimplant 60 with material.

In the embodiment of implant 60 shown in FIG. 26A, where couplinginterface 108 comprises a threaded lumen 118, the delivery catheter 114comprises an outer sheath similar to the sheath described above. Theinner core of this embodiment of the delivery catheter, however,comprises a lumen 166 and a threaded outer surface 168 complementary tothreaded lumen 118 of implant 60. Implant 60 attaches to deliverycatheter 114 by rotating inner core 120 into threaded lumen 118 of theimplant. To resist rotation of implant 60 from frictional forces duringthe attachment or detachment of implant 60, the polygonal cross-sectionof inner surface 150 of outer sheath 146 is capable of forming amechanical interfit with the polygonal cross-section of coupling base116 on implant 60 when outer sheath 146 is extended.

In an alternative embodiment of the delivery system, a guidewire orguide pin having a diameter of about 0.010 inch to about 0.038 inch anda length of about four inches to about eight inches is provided forinsertion into the sinus tarsi. The guidewire is insertable through aneedle inserted into the sinus tarsi. The needle is withdrawn after theguidewire is positioned. An introducer may be passed to further dilatethe passage to the sinus tarsi. The sizing and delivery catheters areadapted for passage over the guidewire into the sinus tarsi. In thisembodiment, both catheters would each have at least two lumens. Onelumen is used to pass the catheter over the guidewire and the otherlumen would be used to inflate the sizing balloon or implant. Theselumens may be oriented in a dual concentric configuration or adjacent toeach other.

One indication for this embodiment of the implant and implantationprocedure is a reducible, hyperpronated, flexible flatfoot. Thesepatients are commonly pediatric, but adults with posterior tibial tendondysfunction and/or hyper-pronation in the absence of subtalar joint andmid tarsal joint arthritis are also potential candidates. FIG. 29 showsone procedure for using an embodiment of the implant comprisespositioning the patient on a table and draping the lateral side of thefoot in the usual sterile fashion known in the art. The insertion sitefor the implant is identified by palpation of bony markers, includingbut not limited to the fibular head, cuboid, talus and calcaneus bones.The lateral opening of the sinus tarsi is identified anterior, medialand inferior to the lateral malleolus or distal head of the fibula.Local anesthesia is injected into the skin and the connective tissueoverlying the insertion site. Anesthetics with epinephrine may be usedto limit bleeding at the insertion site. Alternatively, regional orgeneral anesthesia may be used. The surgeon places the foot in aslightly supinated position to widen the lateral opening of the sinustarsi during the procedure. A needle is inserted at the desired site anda small cannula is passed over the needle. The desired depth ofinsertion is determined by markings on the cannula and assisted byfluoroscopic imaging. The needle is then withdrawn. The cannula may beof “peel-away” type as is known to those with skill in the art. The footwith the inserted cannula is radiographically imaged to facilitatepositioning of the cannula in the sinus tarsi. FIG. 28A illustratessizing catheter 124 with an attached, fluid-filled syringe insertedthrough cannula 122. The foot is then repositioned and held in agenerally neutral alignment. Neutral alignment is defined as the footposition where the lateral aspect of the heel becomes perpendicular tothe leg and the talonavicular joint feels congruous to palpation.Neutral alignment is often, but not always, the position in the range ofmotion where the foot is capable of two-thirds additional supination andone-third additional pronation. Foot alignment can also be checkedradiographically by assessing changes to the cyma lines in the AP andlateral views of the foot, as previously shown in FIGS. 9A and 10A.

Referring to FIG. 28B, balloon tip 126 on sizing catheter 124 isinflated until significant resistance is met. The inflation volume onthe syringe is measured. The surgeon assesses the range of motion andalignment of the foot with the inflated sizing catheter in place. Thisallows the surgeon to estimate the potential changes to the joint and tofacilitate selection of the permanent implant. The surgeon also checksthe quality, range, location and smoothness of joint motion.Radiographic imaging may be performed for additional assessment of thejoint. The cannula is repositioned and/or the sizing balloon volume isadjusted to achieve approximately four degrees of foot eversion. Asnoted previously, approximately one third of the subtalar range shouldbe in the direction of pronation and two-thirds towards supination.Balloon tip 126 is deflated and sizing catheter 124 is withdrawn. FIG.30A shows delivery catheter 114 with selected inflatable implant 60passed through cannula 122 and into sinus tarsi 26. Cannula 122 isoptionally peeled away from the foot. Implant 60 is inflated with atleast one material 58 to the desired volume based upon the inflationvolume measured with sizing catheter 124. Foot alignment and range ofmotion is rechecked by physical exam and/or radiographic imaging. Theinflation volume of implant 60 may be adjusted based upon the results ofthe exam and/or the imaging until the desired talocalcaneal position isachieved. In one embodiment, the surgeon uses the cyma line, incontradistinction to an anterior displaced talonavicular joint, as anindication that a pronated foot has been reduced to a more neutralalignment. Implant 60 is then sealed, if implant 60 is not self-sealing.Referring to FIG. 30B, delivery catheter 114 is detached from implant 60and both catheter 114 and cannula 122 are withdrawn from the patient. Ifnecessary, the insertion site is closed by either suturing or adhesivesand dressed. A splint or cast is applied to the foot.

In an alternative implantation procedure, the material used to inflateimplant 60 to the desired volume is removed from the implant and itsvolume is measured. An equal or similar volume of another materialhaving a different density or characteristics is used to reinflate theimplant. This alternative procedure may be used to obtain a moreaccurate measurement of the sinus tarsi and the volume of finalinflation material to be used where the final inflation material changesvolume as it cures. The volume of the initial fluid used to assess thesinus tarsi is used to calculate the volume of uncured final inflationmaterial to be delivered.

In another alternate method of implanting the device using a guidewire,the patient is placed on a table and the lateral side of the foot isdraped in the usual sterile fashion known in the art. The insertion sitefor the device is identified by palpation of bony markers, including butnot limited to the fibular head, cuboid, talus and calcaneus bones.Local anesthesia is injected into the skin and connective tissueoverlying the insertion site. Anesthetics with epinephrine may be usedto limit bleeding at the insertion site. A large bore needle is insertedat the desired site and a guidewire is passed through the needle.Optionally, a small dilator is passed over the guidewire for enlargingthe pathway to the sinus tarsi. The foot with the inserted guidewire isradiographically imaged to confirm positioning of the guidewire in thesinus tarsi. A catheter with the inflatable implant at the catheter tipis passed over the guidewire and into the sinus tarsi. The implant isinflated to the desired volume. The talo-calcaneal relationship ischecked by physical exam and/or radiographic imaging. The inflationvolume of the implant may be adjusted based upon the results of the examand/or the imaging until the desired talo-calcaneal position isachieved. The surgeon may use the cyma line, in contradistinction to ananterior displaced talo-navicular joint, as an indication that apronated foot has been reduced to a more neutral alignment. The deliverycatheter is detached from the implant and both the catheter andguidewire are withdrawn from the patient. The insertion site is closedby either suturing or adhesives and dressed.

The implant and delivery system described above can also be adapted forinsertion into the first MTP joint of the foot. Referring to FIGS. 31Aand 31B, the implant shape for this embodiment of the invention ispreferably an implant comprising a first concave surface 170 on a firstside of the implant 172 and a second concave surface 174 on a secondside. First concave surface 170 is adapted to contact the distal end ofthe first metatarsal and second concave surface 176 is adapted tocontact the proximal end of the first proximal phalanx of the foot.Other shapes, however, can be used depending upon the particular anatomyand disease of the first MTP joint. The delivery system will generallyhave a shorter length because of the accessibility of the first MTPjoint.

While this invention has been particularly shown and described withreferences to embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the scope of the invention. For all ofthe embodiments described above, the steps of the methods need not beperformed sequentially.

1. A method for treating a patient, comprising: providing an inflatablesubtalar implant; inserting said implant into the sinus tarsi of a foot;and inflating said implant with an inflation material.
 2. The method ofclaim 1, wherein said material is a fluid.
 3. The method of claim 1,wherein said material is a solid.
 4. The method of claim 3, wherein saidsolid comprises microspheres.
 5. The method of claim 1, furthercomprising changing the alignment of the hindfoot.
 6. The method ofclaim 1, wherein said inserting step is performed through a cannulainserted into said sinus tarsi of said patient.
 7. The method of claim1, wherein said inserting step is performed over a guidewire insertedinto said sinus tarsi of said patient.
 8. The method of claim 1, furthercomprising combining multiple agents to form said inflation material. 9.The method of claim 8, wherein said combining step is performed beforesaid inflating step.
 10. The method of claim 8, wherein said combiningstep is performed during said inflating step.
 11. A method for treatinga patient, comprising: providing an inflatable subtalar implant;identifying a foot having a first range of motion; inserting saidimplant into the sinus tarsi of said foot; and adapting said foot to asecond range of motion by inflating said implant.
 12. A method fortreating a patient, comprising: providing an inflatable subtalarimplant; identifying a foot having a first weight-bearing alignment;limiting said foot to a second weight-bearing alignment; inserting saidimplant into a sinus tarsi of a foot; and securing said foot in saidsecond weight-bearing alignment by inflating said implant.
 13. Themethod of claim 12, wherein said first and second weight-bearingalignments are defined by the angle between a first line connecting theedges of an articular surface of a talus and a second line connectingthe edges of an articular surface of a navicular bone.
 14. The method ofclaim 12, wherein said first and second weight-bearing alignments aredefined by the angle between a first line along the long axis of a talusand a second line along the long axis of a first metatarsal bone. 15.The method of claim 12, wherein said first and second weight-bearingalignments are defined by the angle between a first line between theplantar-most point of a calcaneus of a patient and an most inferiorpoint of the distal articular surface of said calcaneus, and a secondline within a horizontal plane of said patient.
 16. The method of claim12, wherein said first and second weight-bearing alignments are definedby the angle between a first line along the plantar border of acalcaneus and a second line along a first midpoint in the body of atalus and a second midpoint in the neck of said talus.
 17. A minimallyinvasive method for treating a patient, comprising: providing aninflatable subtalar implant; inserting said implant into a sinus tarsiof a foot; inflating said implant; changing the range of motion of thesubtalar joint of said foot; and conforming the implant to the shape ofthe sinus tarsi thereby.
 18. A method for treating a patient,comprising: identifying a cyma line in a foot of a patient; smoothingsaid cyma line; and securing said smoothing by inflating an implant inthe sinus tarsi of said foot.
 19. A method of treating a patient,comprising the steps of: accessing a sinus tarsi of a foot through anaccess path having a cross sectional diameter of no more than about 0.5inches, the sinus tarsi having a talus and calcaneus spaced apart by afirst minimum distance; increasing the space between the talus andcalcaneus to a second minimum distance; and restraining the talus andcalcaneus at said second minimum distance.
 20. A method for treating apatient, comprising: providing an inflatable first metatarsal-phalangealjoint implant; inserting said implant into a first metatarsal-phalangealjoint of a foot; and inflating said implant with a fluid.
 21. A subtalarjoint implant, comprising: an inflatable balloon adapted for positioningin the sinus tarsi of a foot.
 22. A foot implant, comprising: aninflatable balloon, wherein said inflatable balloon is adapted forextra-articular positioning in the sinus tarsi of the foot.